Did the timing chain guides last night on my 1990 560SEL with 128,000 miles and when I opened it up I found the top drivers side guide already broken in two pieces just sitting there waiting to fall into the engine! I am sure glad it didn't decide to go when I was flying down the road at 145 mph about a week ago!
If you have a Mercedes V8 and haven't done the guides I would strongly suggest thinking about getting it done.